Dyarbrough

Hi guys,
my electric fan isn’tkicking on, I’ve had it where my 92 Cherokee Laredo has gotten to around 225°. The electric fan is new, I bought one for a 95 grand Cherokee which is compatible and is supposed to have more air flor. Water pump is new, I have a 180° thermostat in, it will kick on when the ac starts and the thermostat sensor is brand new as well. The fan will kick on when I unplug the sensor out of the thermostat. I have also replaced the fuse to the fan. Any ideas?

Griffyorcono

Check your grounds, test and a replace the relay for the fan (just replace it with one that is guaranteed to work, aka BRAND NEW), ohm test your temperature sensor it could be reading way off especially if it isn't a Mopar sensor, check your check engine light it will lead you the right direction and may even say something if the check engine light isn't on when the motor is. Check and lastly if none of these work check out the PCM, may not be activating the fan like it should.

This is everything I can think of, based on some of the tests you have done you may not need to do all of these but I would start with checking the grounds to the temp sensor.

Good luck

bluejeep2001

If the fan turns on when you unplug the sensor then the relay is good as is all power to the fan system. Your 92 runs a separate temp sensor to drive the gauge as compared to the tstat housing sensor which is used for fuel mixture control and fan control. One of them may be way off. I cannot remember if the 92 t-stat sensor has 2 pins in it or just 1 and it "grounds" through the body to the block . Your gauge sender works like that..1 pin and it grounds thru the sensor threads. If only 1 pin then take a meter from the brass body to a good ground...if its more than 10-15 ohm then you have too much sealant/tape on your sensor threads. If 2 pins then it does not use the body as a ground so it doesn't matter. At boiling the sensor resistance from pin to pin or 1 pin to ground should be ballpark 650-700 ish. and the fan should not kick till around 220..ish . The sensor resistance lowers with higher temps

Dyarbrough

mim assuming you’re talking about the one at the back of the block? It only has one pin. I’ll check that one out as well! Thanks!

bluejeep2001

No the one at the back of the block ONLY drives the gauge...it has no control of anything else and yes that one is a single wire. The sensor in the thermostat does fan control but I couldn't remember if it had 1 or 2 pins . My 92 has been dead for 5 or 6 years now and I couldn't remember the details. Either the sensor in the thermostat is off calibration and not turning on fan thru sensor resistance values or your gauge sensor is off calibration and you are never actually reaching 220 ish even though it says you are

Dyarbrough

I ended up buying new oem sensors for the coolant temp sensor and the thermostat sensor, I’ll update if this fixed the issue. I’ve had issues in the past buying autozone sensors

97grand4.0

No such thing as a Cherokee Laredo.

Dyarbrough

for a 1992?

97grand4.0

I stand corrected. Laredo was apparently a Cherokee trim level from 1985 to 1992.

I keep engaging my transfer case before I put my transmission in gear.

And anyone that followed that is really paying attention.

97grand4.0

T stat is 180F? that shows on Rockauto to be Alternate Temperature, the OE temperature is supposed to be a 195 T stat. If your system isn't hot enough you won't be in closed loop and it will likely override the fan relay to try to get hotter. Also you won't run very well because the O2 sensor isn't controlling the fuel flow, ..timing and fuel will be from the map in the computer

BruceB

I agree with 97grand40.... verify your temp by getting a laser temp reader and aiming at the thermostat housing. You may find the engine is not getting hotter than 180 degrees regardless what the gauge states. The temp sensor on the rear of the head is sending to the gauge, the front sensor is sending to the PCM.

97grand4.0

Even better yet, get a scan tool and see what the PCM is actually seeing from the coolant temp sensor in the T stat housing.

bluejeep2001

The 92 is obd1 didnt think you could read engine data on that series

97grand4.0

Ah. Hmm. I thought of that too. I think if it has an O2 sensor it still needs closed loop.
What else is weird that they would even offer the 'alternative' 180 T stat when OE is 195. Must be a high demand for it, like people trying to get the XJ to run cooler.
Ive been looking hard at the radiator design on the xj lately. Went to the junkyard and this xj had to the whole front end ripped off, exposing the radiator. I have said before the radiator just looks very small and it does, to me, even though the cooling system capacity is the same as a zj. So not only did it look small but the whole front of the radiator is covered by ....a transmission cooler. Making it even harder for air to get through! The regular fan, as we know occupies, only the left half of that space. The AR transmission is great but large and must generate mucho heat. And then we have the oddity that the xj oil pressure drops way more than other models when hot...Just my musings....

Dyarbrough

the whole cooking system only home 3 gallons, I’ve thought about upgrading the radiator but I’ve only read horror stories. The o2 sensor is located right where the exhaust manifold and the first down pipe attaches. I’ll check it out